In-situ disinfection by flexible surface dielectric barrier discharge plasma film: discharge modes and mechanisms

In this work, a surface-dielectric-barrier-discharge (SDBD) based flexible plasma film (FPF) was established and tested for in-situ surface disinfection. The discharge product mode (i.e. O-3 mode and NOx mode) was controlled by the applied voltage and verified by in situ gas product quantification. For in situ disinfection, the NOx mode shows significantly higher bactericidal efficiency than the O-3 mode, and the FPF achieves similar to 3.5 logs and >6 logs of bacterial reduction with 3 and 5 min of plasma exposure in the NOx mode, respectively. The underlying mechanism is investigated. In the O-3 mode, the heating effect of the plasma plays either a negligible or moderate role in bacterial inactivation, depending on the applied voltage. In the NOx mode, both high temperature and long-lived species can play a role, while it is speculated that short-lived species are primarily responsible for the high-order bactericidal rate (>3 logs), with atomic oxygen likely playing an important role. As revealed by scanning electron microscopy and Fourier-transform infrared (FT-IR) spectroscopy, the NOx mode can lead to more pronounced bacterial etching and nitrification compared to the O-3 mode, accounting for its superior disinfection performance. By examining the time-dependent FT-IR infrared spectra of treated bacteria, it is found that nitrification is the dominant spectral variation, and the ratio of infrared bands at 1354 and 1654 cm(-1) can serve as a positive indicator of disinfection efficiency. This study can provide deeper insights into the discharge mode, disinfection performance, and bactericidal mechanisms of the SDBD-based FPF, offering guidance for the control, evaluation, and future applications of this technology.